But there is still a second point which explains the remarkable position taken by ancient physicians in relation to magical medicine—namely, the fact that the conception of miracle and magic were essentially different in the ancient world from what they are at present. The belief in the interference of spirits and supernatural beings in terrestrial matters, and the manifestations of their influence exerted in manifold ways—sometimes for good, sometimes for evil—had been widely disseminated from the earliest times, and we encounter them in all periods of classic antiquity. This belief in demons had become incorporated in the systems of many leading philosophers of antiquity. Now if the world were filled with demons the natural consequence was that their activity would manifest itself in various ways. It was necessary, therefore, that man should always be prepared to experience manifestations which more or less violated the customary order of terrestrial happenings, and for this reason nothing that could be styled a miracle really existed for him. A miracle could not be conceived in its full modern sense until it was realized that the course of all natural phenomena was nothing but the expression of eternal and changeless laws. However, it was not until comparatively late that this conception became generally disseminated; thus, for instance, it was considered as self-evident, even in the latest periods of the middle ages and during the first beginnings of modern times, that divine influence could always, and actually did always, cause an alteration in the course of the functions of the body. In fact, there is an amazingly large number of people even in our time who believe this, and for whom, therefore, the conception of miracles, especially of miraculous healing, is to-day on about the same level as that on which it stood in the time of Galen and Alexander of Tralles.